Liquid heater control



Nov. 2l, 1950 J. c. WHITE LIQUID HEATER CONTROL Filed March l1, 1947 n.NN w1 lll WW WN NN IN VEN TOR.

Patented Nov. 21, 1950 UNITED STATESv PATENT OFFICE LIQUID HATR CONTROL.lohn C. White, Madison, Wis.v

Application March 1'1, 1947, Serial No. 733,973

v2 claims. (ci. zel- 62) The invention relates to the control of liquidheaters by which acids and other liquids are heated by the injection ofsteam into a stream of the liquid. This application is a continuation inpart of my copending application Serial Number 547,455, led July 31,1944, now aban doned.

Liquid heaters of the type mentioned are used in various commercialoperations including the heating of acid and pulp mixtures in digestersand cookers in the paper industry. A heater for a pulp digester has beenchosen for exemplifies.- tion herein in aid of effecting disclosure ofthe invention.

In a sulphite process the sulphuric acid which may have a gravity ofabout 1.03, is the circulating medium which must be heated and, foroptimum conditions, must be caused to absorb enough heat during eachcyclethrough a heater as to raise the temperature of the digester orcooker contents from 22 to 23 F. so that after repeated cycling a finaltemperature of 325 F. will be reached, within a digester of the usualsize, in a period of about seven hours. The problem is complicated bythe fact that at the time of the start of a cook the acid temperaturewill be in the neighborhood of 150' to 160 F. with a vapor tension(pressure) about 3.8 lbs. per square inch, absolute, while at the end ofa cook` the acid temperature may be 325 F. with a pressure of 96.16 lbs.absolute.

The rate of rise of temperatureV and pressure` in part will depend, ofcourse, on the rate of circulation and the size of the digester as wellas some other factors but, as above stated, with optimum conditions andthe usual size of digester, the desired temperature and pressure will bereached in about seven hours. Normally the acid is held at thistemperature and pressure for about half an hour or more, circulationthrough the heater being continued for this purpose, and after the cookhas been completed the digester is blown down. The heater thus worksthroughl a temperature range of from, say, 150 F. to 325 F. and acorresponding range of pres-V sures of from 3.8 lbs. to 96.16 lbs.absolute.

The preferred types of heater used forl this work are those designed onthe principle ofY the Giffard injector wherein the liquid enters thesteam and liquid combining tube atY a high velocity around the voutsideof a jet of steam issuing from a conical nozzle High Velocity fortheliquid is necessary to furnish a suicient contact area of acid to absorbthe required heat from the steam. As an example, with an acid pressureon the system of 8O lbs., the acid should enter the combining tube at avelocityv of not less than feet per second. Unless the properrelationship of acid contact area to steam pressure is attained andmaintained, vibration and hammering develop or the heater efliciencydrops. In heaters of the type mentioned the velocity of the cireulatingacid (under pump pressure) at the inlet to the injector is proportionedby adjusting the combining tube to vary the inlet oriiice area until thepoint of most quiet and vibration free operation is attained with arelatively constant pressure steam supply. However, after a rela-Vtively short period of operation the combiningr tube may freeze inposition because of baking of lime and ber in its bearing in the heaterwhereupon no further adjustment can be effect,- ed. Thevelocity of theacid, set up by choking its flow at the inlet, isV partially convertedto pressure head later on, and, With the small in crement due to thesteam action, may be entirely recovered. On a rise of no more than, say,23 F. per cycle, the steam `can impart almost no circulating energy tothe liquid for which reason the liquid circulation must be eiected bypumping although a rise of 40 F. is ordinarily suicient to establish`circulation in a hot Water heating system for buildings.

Steam flow, that is, the volume thereof, from the steam inlet nozzleintoV the combining tube or chamber, is controlled by a valve which, inyturn, is either controlled or adjusted by hand or by relativelyautomatic means such as a thermostatically operated mechanismresponsive, say, to temperature of the acid in the digester. Automaticcontrol is preferred to hand control, of course, but in most casesprovision is made for both as a safety measure since the hand controlmay be operated should the automatic control become inoperative for anyreason. One type of automatic operating mechanism includes an airactuated diaphragm connected through a connecting rod and a bell-cranklever with the stem of the steam control valve so that a movement of thediaphragm in one direction will tend to open the steam valve and amovement in the opposite direction will tend to close the steam valve.This type of control will be illustrated herein.

In a typical installation using a steam valve and control such as abovementioned, the conical valve head shouldy be set with the controller sothat a minimum volume of steam enters the combining chamber at the startof the cook, the controller thereafter effecting continued opening ofthe steam inlet orifice as the process proceeds until, toward the lastoi the cook the valve may be Wide open to admit full volume inlet ofsteam. Since, at the start of a cook, the acid temperature is W, say,lc" F., and has a velocity oi pei'- haps, llii feet per second Vat theliquid inlet orifice, condensation of the steam creates a low pressurearea oi substantial degree adjacent to the downstream end of the valvethereby exerting a strong force on the valve head tending to close thevalve. rfhis iorce therefore is supplementary to and operates in thesaine direction as the steam pressure, and the two forces so createdi'orm a heavy working load on the controller at the start but as thecook progresses and the digester temperature approaches the heatingsteam temperature (at which time the valve may be i'ully open) the loadon the controller decreases.

The controller, in its efforts to hold the temperature rise within itspredetermined or set limits, and under the iniluence of the heavy loadimposed on it, opens and closes the valve so rapidly that it results ina relatively continuous clatter of the valve head against its seat. Thisproduces undesirable noise and vibration, increases wear and tear on thevalve head and seat and other parts and interferes with the accuracy ofcontrol by the controller.

The primary purpose of my invention, therefore, is partially tocounterbalance the forces tending to close the steam inlet valve therebyto eliminate the objectionable conditions mentioned. To this end acounterbalancing chamber is provided about the stem of the steam inletvalve and arranged to have communication with the low pressure area inthe combining tube adjacent to the downstream end of the valve head sothat the pressure effective at the latter place is also eiective in thecounterbalancing chamber. In this chamber a portion of the valve stemserves as a differential piston operative under a pressure drop in thechamber to draw or tending to draw the valve head from its seat, butsince the eiective area of the differential piston is less than theeifective area of the steam nozzle inlet orifice, there will always bean overbalancing force tending to close the Valve although such forcewill be substantially less than otherwise would be the case and thehunting of the valve and the overload thereon and on the controller ispractically eliminated, while the valve and controller operations becomemore sensitive and accurate. This differential effect persistsproportionately throughout the entire range of opening movements of theValve.

In order to avoid stoppage of the passageway (and the entry of acidthereinto) by which communication between the counterbalancing chamberand the low pressure area within the combining tube is established, avery small passage- Way is provided through the wall of thecounterbalancing chamber to the steam supply so that a slight leakage ofsteam into the counterbalancing chamber may occur. Also this smallpassageway or orice permits condensate to drain from thecounterbalancing chamber. It should be observed, however, that the sizeof this passageway or orifice should not be such as materially to aiect(increase) the pressure in the counterba-lance chamber. This,accordingly, constitutes another object of the invention.

Many other important features as well as other advantages and theseveral uses of the invention will become apparent and understood afterreading the following description and claims in connection with theaccompanying drawing in which:

Fig. l is a longitudinal sectional view through an apparatus embodyingmy invention;

Fig. 2 is a transverse sectional View on the line 2 2 of Fig. 1;

Fig. 3 is a similar View on the line 3-3 of Fig. 1; and l Fig. 4 is aplan view of the structure shown in Fig. 3.

On the drawings, reference character 5 indicates the body of the liquidheater within which is mounted the combining tube 6 adapted forlongitudinal adjustment Within the body. VThe tube may be adjustedlongitudinally or" the body, for purposes which will be later explained,by means of a hand operated adjusting lever I xed upon the end of avertical shaft Il provided at its lower end with an arm 9 having a studor pin II engaged with the combining tube, so that actuation of theshaft 8 by the lever I will impart a longitudinal adjusting movement tothe tube. The lever "I may be locked in adjusted position by means of alocknut I2 threaded upon a bolt I3 which passes through the lever 'I andthrough a slot in an underlying sector I4.

The body 5 is shaped to provide a chamber I5 surrounding andcommunicating with the inner or receiving end of the combining tube 6.The body is also shaped to provide a connection I6 communicating withsaid chamber and adapted to be connected with the outlet pipe of acooker, digester or other piece of equipment for which the liquid is tobe heated. The outer end of the body is anged, as indicated at I1, forconnection with a pipe constituting the inlet pipe for the cooker or thelike.

In operation the liquid to be heated is recirculated through the heaterand cooker, entering the heater from the cooker through connection I6and returning to the cooker from the heater through the pipe (not shown)connected to the flange II of the body and into which the delivery endof the combining tube 6 extends. A pump (not shown) in the line betweenthe digester or other apparatus and connection I6, serves to effeet theliquid circulation.

The opposite end of the body is connected by bolts I8 with a flanged TI9 including a flanged connection ZI adapted to be connected with a pipeleading from a suitable source of steam under pressure. The body andconnected end of the T are constructed to receive the valve guide 22 andthe steam nozzle 23 which are clamped in position upon tightening of thebolts I8. A round tapered member 24 has a leak-tight nt with the hub 25of the valve guide 22, and at its other end has a similar t with the hub26 of an end piece 2'! which is bolted to and closes that end of the Tmember I9. A chamber 28 within the cylindrical member 24 is therebyformed, which will be referred to herein as the balancing chamber.

The hub 25 and the guide are hollow, as shown, providing a bore withinwhich a piston 29 snugly but slidingly fits. At its outer end the pistoncarries the frusto-conical valve SI adapted to close against the seat 32surrounding the discharge opening of the steam nozzle 23. The inner endof the piston 29 is threadedly connected with the valve stem :i3extending longitudinally within the balancing chamber and outwardlythrough the stuing box 34 carried by the head 2l. The outer portion ofthe stem is threaded, as indicated at 35, for cooperation with a handwheel 30,1: bymanipulati'onvr` of which longitudinal move'-- rent may b'imparted to theV stein 33. A link 31 connected to the extremity of thestem 33 connects the stem with an operating lever 3S, which in' turn isYadapted to be actuated by a controller 39, thermostatically or pressureoperated in a manner well known in the art, for the purpose of adjustingthe position of the valve 3| to regulate the volume supply of steamdelivered from the nozzle so as to produce the predetermined temperaturerise in the fluid being heated.

As shown on the drawing, the steam valve 3| is hollow and provided witha passage 4| opening at the small end of the valve into the combiningtube. The piston 29 guided in the hub 25 of the guide 22is also hollow,providing a passage communicating with the passage in valve 3| and witha passage 43 in the end portion of the stem threaded into the piston.Communication between this passage 43 and the balancing chamber 28 isafforded by a plurality of radial passages 44. It will be apparent,therefore, that through the passages 4|, 42, 43 and 44 communication isestablished between the balancing chamber 28 and the area adjacent thesmall end of the valve. The perimeter of the piston 29 and that portionof the stem 33 passing through the end plate 21 may be lubricated torender their movement easy and to protect against leakage. Lubricantpassages 45 and 43 adapted to accommodate the connection of pressuregrease guns are provided for that purpose.

It will be understood by those skilled in this art that the fluid to beheated, entering the body of the heater through the connection I6, isdelivered under pressure into the combining tube 6 at the inner endthereof around the tapered steam nozzle 23. The liquid, therefore,enters the tube in a stream substantially conical in shape. The steamdelivered by the steam nozzle, in an amount determined by the proximityof the perimeter of the tapered valve 3| to the surrounding seat 32, isalso in a stream of substantially conical shape, but inside the conicalstream of fluid with which it combines. In the early stages of a cook,the admission of the fluid to the combining tube at high velocity andcondensation of steam therein produces a zone of low, or negative,pressure within the cone upon its entrance to the tube, and into thiscone the entering steam is projected.

As the acid or other liquid being heated rises in temperature, thecontroller tends to open the steam inlet valve member 3| wider and widersince more and more steam must be admitted to effect each succeedingincrement of temperature rise of the liquid. But, of course, as thistakes place the degree or intensity of the low pressure area in thecombining tube adjacent to the nozzle or valve member 3| will becomeless and less which, in turn, progressively lessens the effectiveclosing force on the valve and the counterbalancing effect of chamber28. Because there must always be a positive pressure tending to closethe steam inlet valve, the counterbalancing piston should have aneffective area of not more than about 65% to '70% of the area of thesteam nozzle or inlet orifice; 65% is preferred.

This low pressure area, which may or may not be a minus atmosphericpressure, tends to pull the valve toward the right (Fig. 1) toward itsseat 32, and this tendency to movement is augmented by the steampressure on the back face of the valve. Under certain conditions,therefore, depending upon the temperature of the liquid being heated,upon the extent-y1 of tem-pera: ture rise to beA produced in the heater,upon relative' pressurerv responsive areas, and upon other factors the'pull exerted by the stern' 33 upon the controller 39 amounts to severalhundred pounds. By applying this low pressure', however, to the inner'endy of piston 29, it counteracts the pull or partially counterbalancesthe valve so that the strain exerted upon the controller is verymaterially red-uced.l This renders the adjusting movement much easierand contributes towardaccuracy of control and uniformity of resultsproduced.; The degree of counterbalancing action attained may be variedin different designs by increasing or diminishing the end area of thepiston exposed in the" balancing chamber 28, other proportions remainingthe same.

The counterbalancing chamber wall, that is, the conical wall 24 has asmall aperture or perforation 41 at its low point which not only mayserve to drain the chamber but also permits the entry of a smallquantity of steam which may serve to scour the passageways 4|, 42, 43and 44 and prevent acid and ber or other matter from entering andclogging such passageways. It may also be desirable to provide a secondaperture or perforation 48 of about the same size of that at 41, for theadmission of steam but if such aperture is located at a high point asshown in Fig. 1, it will not serve also as a drain.

It is believed my invention and its principle of operation will beunderstood from the foregoing Without further description, and it willbe manifest that the structural details illustrated and described may bevaried Within considerable limits without departing from the essence ofthe invention as defined in the following claims.

I claim:

1. In a liquid heating apparatus having a combining tube, means fordelivering a stream of liquid in the form of a hollow cone into saidtube, a relatively fixed nozzle providing a valve seat adjacent to itsoutlet end and adapted to discharge into said hollow stream, a taperedvalve projecting from within said nozzle into the tube and movabletoward and from said seat for controlling the discharge from saidnozzle, means for supplying steam to be discharged from said nozzleunder control of said valve, the tip of said valve normally beingdisposed within the hollow conical portion of said liquid stream, meansoperatively associated with said valve for moving the same positivelyfrom said seat, and means for counterbalancing a portion of the forcestending to close said valve, said means comprising a balancing chamber,a piston upon which the valve is mounted presenting a pressure area tothe interior of the chamber, and a passage through the valve and pistonestablishing communication between the area at the tip of said valve andsaid chamber.

2. In a liquid heating apparatus having a liquid-steam contact chamber,means providing a liquid inlet of annular form for liquid entering thechamber, and means providing a single steam outlet orifice disposedconcentrically within the liquid inlet, said steam outlet meansincluding an orice defined by a valve seat, a valve mechanism forcontrolling the emission of steam from said orifice into said chambercomprising, a valve stem guide, a valve stem mounted in said guide formovements in the direction of the stem axis, a conical valve headcarried by said stem and cooperative with said valve seat, the base ofthe cone being disposed on the upstream side of said orice and the smallend of the cone normally being disposed on the downstream side of saidorice and within said contact chamber, means providing a walled Valvebalancing chamber, a passageway communicating between said balancingchamber and the interior of said contact chamber adjacent to said smallend of said valve head, means for moving said stem to move said headtoward and from said seat, a valve balancing piston in said balancingchamber and connected with said stem, said piston being constructed andarranged to oi-set a substantial portion of the eiect of reducedpressure in said contact chamber adjacent to the small end of said valvehead tending to close said valve head against said Seat whereby toreduce the effect of forces acting on said stem moving means in adirection tending to move said valve toward the closed position, and anaperture of small area connecting said counterbalancing chamber with aplace of drainage for said chamber, said aperture area being of suchsmall size as to have a relatively immaterial effect on the pressurewithin said chamber.

JOHN C. WHITE.

REFERENCES CITED The foliowing references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 615,914 Schutte Dec. 13, 18981,243,999 Snediker Oct. 23, 1917 2,372,533 Torbett Mar. 27, 1945

